Tripping device for circuit breakers

ABSTRACT

A tripping device (1) for circuit breakers comprising a thermally influenceable wire-shaped tripping element (4) is presented, one end of which is attached to a rotatably supported tripping lever (3) which is under spring force and the other end of which is fixed in location. The thermally influenced lateral movement at one end of the tripping element (4) causes the unlatching of the circuit breaker. At the free end of the tripping lever (3), a locking element (11) is provided which engages a cam (10) of a contact lever (2) which is under spring force, in such a manner that the circuit breaker is switched off both with contraction and with expansion of the tripping element (4).

The invention relates to a tripping device for circuit breakersaccording to the precharacterizing clause of Claim 1. Such a trippingdevice is known, for example, from CH-A-616270. In this document, athermoelectric switch comprising a tripping element of a memory alloywith two-way effect is known. The switch possesses at least one clampingdevice which acts in conjunction with the tripping element and the forceof which, which acts on the tripping element, is used for defining thetemperature of the switching process. In this arrangement, the trippingelement has the dual function of slow- and of fast-acting trippingelements. In a special embodiment, the tripping element is a wire ofmemory alloy. The actual contact of the switch is operated via acomplicated switching mechanism comprising several tension andcompression springs.

The invention is then based on the object of creating a tripping devicefor circuit breakers of the type mentioned above, in which arrangementthe switching mechanism is particularly simple and the tripping elementcan be both a wire of a memory alloy and a wire of a thermally expandingmetal. It should also be unimportant whether a memory alloy according tothe one-way or two-way effect is used.

In a tripping device of the abovementioned type, this object is achievedby the features of Claim 1. The tripping device according to theinvention has the great advantage that the tripping mechanism isdesigned to be particularly simple and enables both tripping withcontraction and with expansion of the wire-shaped tripping element. In aparticular embodiment according to Claim 2, a compression spring isarranged between the tripping lever and a housing rib. As a result, thewire-shaped tripping element is always stretched. If a thermallyexpanding wire is used according to Claim 3, a precisely determinedthermally dependent length is given due to the reversible andreproducible thermal effect of the wire. The temperature-dependentlength is also always known if a memory alloy--particularly with two-wayeffect--according to Claim 4 is used. If, in the above cases, the wirebreaks due to careless handling, the circuit breaker is also tripped. Ifwires of memory alloy according to the one-way effect are used astripping element and if it is required that the circuit breaker shouldswitch on again after a fault, a stop is required in the housing.Nevertheless, in order to ensure tripping in the case of a wire break,the intermediate lever with additional compression spring according toClaim 5 or the transmission element according to one of Claims 6, 7 or 8are provided.

Further advantages of the invention are obtained from the descriptionfollowing. In this description, the invention is explained in greaterdetail with reference to an illustrative embodiment shown in thedrawing, in which:

FIG. 1 shows a particularly simple embodiment of a tripping device forcircuit breakers,

FIG. 2 shows a tripping device with intermediate lever and additionalcompression spring,

FIG. 3 shows a tripping device comprising a first variant of atransmission element, and

FIG. 4 shows a tripping device comprising a second variant of atransmission element.

The same reference numbers are used for the same elements in thefigures.

In FIG. 1, the tripping device 1 of a circuit breaker is shown insection. The structure of such a circuit breaker is known per se and canbe seen, for example, in Swiss Patent Application No. 03 147/87-0. Thetripping device 1 consists of a contact lever 2, a spring-loadedtripping lever 3 and a wire-shaped tripping element 4. The trippingelement 4 is fixed in location with its end (not shown) and attached tothe tripping lever 3 with its other end. The tripping lever 3 isrotatably supported on a linking piece (only partly visible). A leafspring 6 is permanently joined to the linking piece 5 and forms theactual contact of the circuit breaker with its other end. In the housingwall 7 of the circuit breaker, a housing rib 8 in the form of an openrectangle (U shape) is provided. A compression spring 9 is arrangedbetween the housing rib 8 and the tripping lever 3. The end of thecontact lever 2 is bent away in the form of an angle and has a cam 10(shown dashed) on the reverse side. A locking element 11, which isformed by a protruding piece 12 of a bent-away part of the end (alsoshown dashed), is provided at the free end of the tripping lever 3. Thewire-shaped tripping element 4 can be a thermally expanding metal wire,for example, or a wire of a memory alloy, as is known, for example, fromCH-A-616270.

The above tripping device operates as follows:

1. If the tripping element is a thermally expanding wire, the wire isheated by an overcurrent or a part thereof and expands. The protrudingpiece 12 of the locking element 11 slides off the cam 10 and the contactlever 2 jumps upward due to the spring loading of the leaf spring 6: thecontacts open.

2. If the tripping element is a wire of a memory alloy, the wirecontracts with an overcurrent (or a part thereof) and the contact lever2 is released again. The compression spring 9 in this arrangement isdimensioned in such a manner that a deformation of the wire 4 is givenin the cold condition. For this purpose, it is desirable to provide astop, not shown here, in the housing on the right of the tripping lever3. However, the force of the compression spring 9 is weak enough for thecontraction of the wire 4 on heating to be ensured.

In FIG. 2, a tripping device 1 with an intermediate lever 13 and anadditional compression spring 14 is shown which is of weaker dimensionsthan the compression spring 9. The intermediate lever 13 is U-shaped andalso rotatably supported with one leg in the linking piece 5. Theshoulder of the intermediate lever 13 is elongated towards the bottomand pressed against a square stop 15 of the housing wall 7 under thespring force of the compression spring 9. The other leg of theintermediate lever 13 rests on the tripping lever 3. The additionalcompression spring 14 is arranged between the shoulder of theintermediate lever 13 and the tripping lever 3. To provide the greatestforce transmission, the compression spring 14 is located close to theother leg of the intermediate lever 13. Naturally, it can also beinstalled in a different location.

This embodiment of the tripping device 1 is provided for wires of amemory alloy. In the case of overcurrent, the operation is the same asdescribed above. If then the wire breaks due to careless handling of thecircuit breaker - for example dropping -, the tripping lever 3 ispressed towards the right by means of the additional compression spring14 and the contact lever 2 is released.

FIG. 3 shows another variant of the tripping device 1 with atransmission element 16 without additional compression spring (compareabove). The transmission element 16 is also U-shaped but here rests onthe tripping lever 3 under the pressure of the compression spring 9. Onehalf of the shoulder of the transmission element 16 is elongated towardsthe bottom with a bent-away guide part 17 which, together with theadjacent leg of the transmission element 16, encircles a pin 18 in thehousing wall 7. In the case of overcurrent--or the case of a shortcircuit--the transmission element 16 is integrally connected to thetripping lever 3. In this arrangement, the pin 18 is used as guide forthe transmission element 16. In the case of a break of the wire 4 of amemory alloy, the pin 18 is then the pivot point for the transmissionelement 16 which rotates clockwise under the pressure of the compressionspring 9 and presses the tripping lever 3 to the right. The contactlever 2 is thus released again.

FIG. 4 shows another variant of the transmission element 16 of thetripping device 1. For the sake of simplicity, the contact lever 2 hasbeen omitted here. The transmission element 16 is essentially arod-shaped plate, the top end 19 of which is bent away towards the rightand rests in a wide opening 20 (shown dashed) of the tripping lever 3.This opening 20 prevents the transmission element 16 from slippingupwards (that is to say out of the plane of the drawing). The bottom endof the transmission element 16 is provided with a guide cam 21 whichprojects into the plane of the drawing and which is carried in a guideslot 22 in the housing wall 7. The guide slot 22 is closed on the rightby means of a stop pin 23. The width of the guide cam 21 is much lessthan the width of the guide slot 22, as a result of which the guide cam21 can be rotated to a limited extent in the guide slot 22.

The tripping device 1 operates as before. If then the wire 4 breaks, thetransmission element 16 is rotated to the right around the stop pin 23by the pressure of the compression spring 9, as a result of which thetop end 19 also rotates the tripping lever 3 to the right and thecircuit breaker is tripped.

I claim:
 1. Tripping device for a circuit breaker having a housing and aswitched-on position and a switched-off position, the tripping devicecomprising:a wire-shaped tripping element having two opposite ends and alength between said ends, said length being thermally influenceable; atripping lever being under spring force and having a free end andanother end, said other end being rotatably supported in said housing; acontact lever being as well under spring force; one of said ends of saidtripping element being attached to said free end of said tripping lever,the other end of said ends of said tripping element being fixed in saidhousing; a compression spring being arranged between a housing rib andsaid tripping lever, which always stretches said tripping element, onend of said tripping element being attached to said free end of saidtripping lever; said contact lever being latched in said switched-onposition of said circuit breaker with said free end of said trippinglever; and said tripping lever and said contact lever being unlatchedand said circuit breaker being switched from its switched-on to itsswitched-off position both with contraction and with expansion of saidtripping element.
 2. Tripping device for circuit breakers according toclaim 1, characterized in that said tripping element is a thermallyexpanding wire or a fusible wire.
 3. Tripping device for circuitbreakers according to claim 1, characterized in that said trippingelement is a wire of a memory alloy.
 4. Tripping device for circuitbreakers according to claim 3, characterized in that, between saidcompression spring and said tripping lever, a U-shaped intermediatelever is provided, one leg of which is supported close to said trippinglever and the other leg of which rests on said tripping lever, that astop is provided in said housing, on which said intermediate lever issupported with an elongated part of its shoulder, and that an additionalcompression spring is arranged between said intermediate lever and saidtripping lever.
 5. Tripping device for circuit breakers according toclaim 3, characterized in that, between said compression spring and saidtripping lever, a transmission element is provided which is supportedagainst said tripping lever and is carried on one side in the housingwall, and that a pin is provided which is normally used as stop andwhich provides the possibility of a rotational movement of saidtransmission element in the case of a break of said tripping element. 6.Tripping device for circuit breakers according to claim 5, characterizedin that said transmission element is U-shaped and its shoulder iselongated with a bent-away guide part in the area of said pin. 7.Tripping device for a circuit breaker having a housing and a switched-onposition and a switched-off position, the tripping device comprising:awire-shaped tripping element having two opposite end and a lengthbetween said ends, said length being thermally influenceable; a trippinglever being under spring force and having a free end and another end,said other end being rotatably supported in said housing; a contactlever being as well under spring force; one of said ends of saidtripping element being attached to said free end of said tripping lever,the other end of said ends of said tripping element being fixed in saidhousing; said contact lever being latched in said switched-on positionof said circuit breaker with said free end of said tripping lever; andsaid tripping lever and said contact lever being unlatched and saidcircuit breaker being switched from its switched-on to its switched-offposition upon contraction of said tripping element, said tripping leverand said contact lever being unlatched and said circuit breaker beingswitched from its switched-on to its switched-off position uponexpansion of said tripping element.
 8. A tripping device for a circuitbreaker having a switched-on condition and a switched-off condition,said tripping device comprising:a housing; a spring biased trippinglever rotatably supported in said housing; a movable contact leverhaving a first position in latched engagement with said tripping leverand being biased to a second position out of latched engagement withsaid tripping lever; means for latching said contact lever in said firstposition constituting said switched-on condition of said circuitbreaker; a wire-shaped tripping element having two opposite ends and alength between said ends, said length changing in response totemperature changes, one of said ends of said tripping element beingattached to said tripping lever, the other end of said tripping elementbeing fixed in said housing; and said tripping element upon expansioncausing rotation of said tripping lever out of latched engagement withsaid contact lever to release said contact lever form said firstposition, said tripping element upon contraction causing rotation ofsaid tripping lever out of latched engagement with said contact lever torelease said contact lever from said first position.
 9. A trippingdevice as defined in claim 8 wherein said tripping element is breakableto cause rotation of said tripping lever out of latched engagement withsaid contact lever.